The ultimate goal of this proposal is to examine conformation changes at specific locations within smooth muscle myosin using intrinsic tryptophan fluorescence. Smooth muscle myosin constructs will be genetically engineered to contain a single tryptophan at the desired site of interest, which will provide a unique intrinsic fluorescence signal reporting local conformational and structural changes in response to nucleotide binding, ATP hydrolysis, and actin-binding. These experiments are complementary to the ongoing structural studies in the field, allowing us to explicitly test predictions about domain movements and structural arrangements during critical steps in the contractile cycle smooth muscle myosin. Thus we will be able to correlate structural changes in myosin with functional consequences, which relates directly to certain cardiovascular disease. For example, FHC (familial hypertrophic cardiomyopathy) is an inherited, often lethal disease caused by point mutations at key structures within myosin critical to its proper functioning as a molecular motor. We will be examining structural changes in myosin in regions of the molecule directly impacted by mutations that underlie FHC. This will lead to a better understanding of the disease, and thus to better treatment options as well. Therefore, this proposal offers a unique opportunity to critically test fundamental questions about the molecular mechanism of muscle contraction that have not been previously accessible by other spectroscopic probe studies, and the results will have important implications for serious disease states such as FHC.